1. Handling the Bunsen burner

a) Don’t work with a burner if the rubber tubing connecting it to the gas tap is damaged or loose;

b) don’t keep the gas tap open while waiting to the lighter;

c) close the gate valve at the end of the laboratory session;

d) if you smell the gas while the tap is closed, inform the instructor immediately.

2. Handling chemical reagents

a) Be careful with corrosive substances (like acids, bases, organic solvents), and particularly careful with their concentrated solutions;

b) if a corrosive substance is dropped on your skin, wash it immediately with water and inform the instructor without delay;

c) if you dilute concentrated sulfuric acid always pour acid to water; newer do the opposite;

d) use spatulas for taking solid reagents - not hands;

e) never close a test tube with a finger - use a cork;

f) don’t taste anything in the laboratory;

g) if you need to smell a substance don’t put your nose into the container; keep the container at some distance and by waving motions of your palm above the mouth of the container send the vapors of the substance towards your nose;

h) reactions involving dangerous or unpleasant odors are to be performed in a hood.

3. Handling glassware

a) Hold the glassware firmly but not squeezing it;

b) do not use broken or cracked glassware;

c) if the glassware is accidently broken, the remainings must be swept to the waste bin immediately.

4. Heating procedure

a) The mouth of a test tube mustn’t point at yourself or anybody else;

b) don’t stand too close to the apparatus in which material is being heated, but never leave it;

c) don’t hold a test tube in your hands while heating, use test tube holders.

Seminar 1 chemical equivalent. Law of equivalents

According to the law of equivalents, all the chemicals react with each other in the amounts which are proportional to their chemical equivalents.

Chemical equivalent is the amount of a substance (in moles) which can react with 1 mole of hydrogen atoms or replace its same amount from a chemical compound.

Equivalent mass, М_E is the mass of one equivalent of a substance expressed in grams per mole.

Calculation of equivalent masses if compounds of different classes can be performed using the following formulae:

(i) elements in free state and in chemical compounds:

М_E = М / V (V is valency of the element)

(ii) acids and bases: М_E = М / n (n is basidity of the acid or acidity of the base, means number of Н⁺ or ОН^- ions)

(iii) oxides and salts: М_E = М / p q ( p is number od metallic atoms and q is their valency)

Number of equivalents n_E = m / M_E ( m is mass of the sample).

For gaseous substances

n_E = V⁰ / V_E⁰ (V⁰ is molar volume of the gas under normal conditions, V⁰ = 22.4 l  mole^-1)

V_E⁰ is equivalent volume of the gas, means the volume which is occupied by one equivalent of a gas under normal conditions.

Possible ways of mathematical expression of law of equivalents:

n_E1= n_E2 ; M₁ / M_{E 1} = М₂ / M_{E 2} ; V⁰₁ / V_E⁰₁ = V⁰₂ / V_E⁰₂